Is it possible to drive the length of hair particles via texture using Cycles?
It works the same way for cycles. Also if you have an animated texture (image sequence or procedural) the animation will effect the length as well.


In the Textures section of the Particle settings for your Particle system, add a new texture.

Now in the Texture tab, change the Influence to Length.



This animation was made by animating the Size on the Distorted Noise texture that is controlling the length of the particles.